In a mobile communication system employing the LTE (Long Term Evolution) system, a radio base station eNB is configured to transmit a MIB (Master Information Block) to a mobile station UE via a BCH (Broadcast Channel), and to transmit multiple types of system information to the mobile station UE via a DL-SCH (Downlink Shared Channel) as shown in FIG. 2.
Here, multiple SIB (System Information Block) 1 to SIB8 are mapped to the system information SI.
SIB1 includes information needed to judge whether or not to allow a mobile station UE to enter in standby mode, such as a PLMN-ID and a cell ID, and is always mapped to a first type of system information SI (System Information)-1.
Meanwhile, SIB2 to SIB8 are grouped and mapped respectively to different types of system information SI-2 and following signs.
It may be considered that each of the SIBs is a message including a specific information element, and that SI is a container for transporting each SIB.
SIB1 mapped to the first type of system information SI-1 is configured to broadcast scheduling information on the different types of system information SI-2 and following signs and to broadcast a transmission cycle T of each type of SI. Additionally, SIB1 is configured to broadcast mapping information between SIBs and SI.
A transmission cycle of the first type of system information SI-1 is fixed to 80 ms. Note that the first type of system information SI-1 can be transmitted repeatedly within 80 ms.
Meanwhile, transmission cycles of the different types of system information SI-2 and following signs are variable, and are assumed to be, for example, in a range of approximately 80 ms to 1.28 s.
As shown in FIG. 1(a), the radio base station eNB is configured to transmit each type of system information in a radio frame having a frame number SFN and satisfying “SFN mod(T/10)=0”. Here, “T” is a transmission cycle of each type of system information. In case of SI-1, T is 80 ms.
Moreover, as shown in FIG. 1(b), the radio base station eNB is configured to transmit the first type of system information SI-1 in the sixth sub-frame in the radio frame satisfying “SFN mod T=0” via the DL-SCH.
In addition, the radio base station eNB is configured to determine a transmission sub-frame in a transmission radio frame (the radio frame SFN=0 in the example of FIG. 1(b)) for each of the different types of system information SI-2 and following signs on the basis of the scheduling information included in the first type of system information SI-1 (or SIB1).
Note that, as shown in FIG. 1(c), the radio base station eNB may be configured to repeatedly transmit each type of system information SI within a window.
However, in a conventional mobile communication system employing the LTE system, the radio base station eNB is configured to transmit each type of system information SI in the radio frame with the frame number SFN satisfying “SFN mod(T/10)=0”. Accordingly, as shown in FIG. 1(a), there is a problem that the multiple types of system information SI are transmitted in a concentrated manner in a radio frame with a specific SFN.
Additionally, a conventional mobile communication system employing the LTE system has a problem that “Persistent Resource Allocation” such as one in VoIP becomes difficult to perform when many of the sub-frames in the radio frame with the frame number SFN satisfying “SFN mod(T/10)=0” are used for the multiple types of system information SI.
“Persistent Resource Allocation” is a scheme in which a Physical Resource Block (PRB) at a fixed frequency position is periodically (for example, a 20 ms cycle at which the VoIP packet arrives) allocated to a certain mobile station UE. This scheme allows reduction in overhead of a control channel (Physical Downlink Control Channel) which performs PRB allocation and MCS control.
“Persistent Resource Allocation” is particularly effective in reducing the overhead of a control channel when applied to a traffic in which packets of approximately the same size arrive periodically as in VoIP.
However, in order to effectively use “Persistent Resource Allocation,” there is a need to always keep a particular PRB vacant at a cycle of PRB allocation.
For example, when a large amount of system information SI is transmitted at a cycle of 320 ms, PRB amount applicable for “Persistent Resource Allocation” is significantly limited.